1. Field of the Invention
The present invention relates to a control system and method for a semi-automatic mechanical transmission system, including a manually operated shift selector movable in a first direction to request upshifting and in a second direction to request downshifting, for automatically controlling the changing or shifting of transmission gear ratios on a vehicle, while leaving the vehicle driver or operator some residual measure of control. In particular, the present invention relates to a control system and method for the semi-automatic control of a mechanical change gear transmission including means for automatically executing automatically determined and displayed allowable driver selected transmission ratio shifts. Preferably, automatic shift implementation of driven selected shifts includes automatic control of the vehicle master clutch and, in one embodiment, a clutch pedal is provided and the master clutch operation is automated in all but start from stop situations. More particularly, the present invention relates to a system and method for controlling a semi-automatic mechanical transmission wherein under rolling start conditions (i.e., the vehicle ground speed exceeds a minimum reference value and the transmission is in neutral and, alternatively, the master clutch is disengaged), a single upshift request is interpreted as a request for a direct shift into a rolling start ratio (GR.sub.RS) determined as a function of current or expected vehicle ground speed.
2. Description of the Prior Art
Fully automatic transmission systems, both for heavy-duty vehicles such as heavy-duty trucks and/or coaches, and for automobiles, that sense throttle openings or positions, vehicle speeds, engine speeds and the like, and automatically shift the vehicle transmission in accordance therewith, are well known in the prior art. Such fully automatic change gear transmissions include transmissions wherein pressurized fluid is utilized to frictionally engage one or more members to other members or to a ground to achieve a selected gear ratio and automated mechanical transmissions utilizing electronic, hydraulic and/or pneumatic logic and actuators to engage and disengage mechanical (i.e., positive) clutches to achieve a desired gear ratio. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 3,961,546; 4,081,065; 4,361,060; 5,050,079 and 5,109,729, the disclosures of which are incorporated herein by reference.
Such fully automatic change gear transmissions can be unacceptably expensive, particularly for the largest heavy-duty vehicles which are not typically sold in high volumes. Moreover, many vehicle operators like to control the selection of the gear ratios, particularly since they can see and/or know the nature of the road ahead and/or of the load being carried.
These drawbacks have been minimized by providing a semi-automatic mechanical transmission control wherein automatic changing between a plurality of gear ratios is provided while normally permitting the driver to choose when to make a particular gear ratio change and whether to select the immediately consecutive ratio up or down or to skip one or more ratios. Examples of such a semi-automatic mechanical transmission control can be seen by reference to U.S. Pat. Nos. 4,648,290; 4,800,360; 4,930,081 and 4,930,078, the disclosures of which are incorporated herein by reference.
While the above-described semi-automatic mechanical transmission control does provide a very desirable semi-automatic control, the control was subject to improvement as, if the driver or operator desired a shift from neutral into a selected transmission rolling start ratio while the vehicle was in motion, the driver was required to identify the appropriate rolling start ratio, to calculate the number of steps from neutral to the appropriate rolling start ratio and to then move the selector lever that number of times in the upshift direction. This was particularly a concern in modern mechanical transmissions for heavy-duty vehicles which may have 9, 10, 12, 13, 16 or 18 forward speed ratios and wherein any one of the first seven ratios may be appropriate rolling start ratios under certain conditions. Examples of such multi-speed mechanical transmissions may be seen by reference to U.S. Pat. Nos. 4,735,109 and 4,754,665, the disclosures of which are incorporated herein by reference.